The technology disclosed in the present specification relates to an image projection device capable of performing three-dimensional measurement by photographing a projection image with a camera and a calibration method thereof. There is known a three-dimensional measurement device combining a projector and a camera. In such a kind of device, a projector projects a known pattern image on an object, and the object on which the pattern image is projected is photographed with a camera. Then, the photographed image is subjected to image processing, thereby three-dimensional information of the object can be obtained.
In the device combining a projector and a camera, it is necessary to perform calibration of parameters regarding both the projector and the camera. The estimation of parameters with high accuracy has a problem of long man-hours for adjustment. For example, the method for projecting a calibration pattern using a calibration marker attached on a plane mirror, a screen, and a projection device is proposed for a three-dimensional form measurement device capable of performing calibration of projector parameters and camera parameters using only the inner structure of the three-dimensional measurement device without requiring arrangement of a special marker in calibration, by embedding a reference object for calibration in the system and automatically calculating world coordinates using a length of the plane mirror that is an invariant (see JP 2013-214206A, for example).
Moreover, in the projector calibration, there is proposed a three-dimensional form measurement device capable of preventing projector parameters from being inaccurate by using a group of intersection coordinates of a horizontal slit pattern and a vertical slit pattern as image coordinates used for projector calibration without including therein coordinates outside the image coordinate range used in camera calibration (see JP 2007-309660A, for example).